Enable the ability to use Godot as a subview within an Android app

platform/android/java/app/src/com/godot/game/GodotApp.java

@@ -30,11 +30,11 @@
 
 package com.godot.game;
 
-import org.godotengine.godot.Godot;
+import org.godotengine.godot.FullScreenGodotApp;
 
 /**
  * Template activity for Godot Android custom builds.
  * Feel free to extend and modify this class for your custom logic.
  */
-public class GodotApp extends Godot {
+public class GodotApp extends FullScreenGodotApp {
 }

platform/android/java/lib/res/layout/godot_app_layout.xml

@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="utf-8"?>
+<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
+	android:id="@+id/godot_fragment_container"
+	android:layout_width="match_parent"
+	android:layout_height="match_parent" />

platform/android/java/lib/src/org/godotengine/godot/FullScreenGodotApp.java

@@ -0,0 +1,79 @@
+/*************************************************************************/
+/*  FullScreenGodotApp.java                                              */
+/*************************************************************************/
+/*                       This file is part of:                           */
+/*                           GODOT ENGINE                                */
+/*                      https://godotengine.org                          */
+/*************************************************************************/
+/* Copyright (c) 2007-2020 Juan Linietsky, Ariel Manzur.                 */
+/* Copyright (c) 2014-2020 Godot Engine contributors (cf. AUTHORS.md).   */
+/*                                                                       */
+/* Permission is hereby granted, free of charge, to any person obtaining */
+/* a copy of this software and associated documentation files (the       */
+/* "Software"), to deal in the Software without restriction, including   */
+/* without limitation the rights to use, copy, modify, merge, publish,   */
+/* distribute, sublicense, and/or sell copies of the Software, and to    */
+/* permit persons to whom the Software is furnished to do so, subject to */
+/* the following conditions:                                             */
+/*                                                                       */
+/* The above copyright notice and this permission notice shall be        */
+/* included in all copies or substantial portions of the Software.       */
+/*                                                                       */
+/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,       */
+/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF    */
+/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.*/
+/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY  */
+/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,  */
+/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE     */
+/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
+/*************************************************************************/
+
+package org.godotengine.godot;
+
+import android.content.Intent;
+import android.os.Bundle;
+import android.view.KeyEvent;
+
+import androidx.fragment.app.FragmentActivity;
+
+/**
+ * Base activity for Android apps intending to use Godot as the primary and only screen.
+ *
+ * It's also a reference implementation for how to setup and use the {@link Godot} fragment
+ * within an Android app.
+ */
+public abstract class FullScreenGodotApp extends FragmentActivity {
+	protected Godot godotFragment;
+
+	@Override
+	public void onCreate(Bundle savedInstanceState) {
+		super.onCreate(savedInstanceState);
+		setContentView(R.layout.godot_app_layout);
+		godotFragment = new Godot();
+		getSupportFragmentManager().beginTransaction().replace(R.id.godot_fragment_container, godotFragment).setPrimaryNavigationFragment(godotFragment).commitNowAllowingStateLoss();
+	}
+
+	@Override
+	public void onNewIntent(Intent intent) {
+		if (godotFragment != null) {
+			godotFragment.onNewIntent(intent);
+		}
+	}
+
+	@Override
+	public void onBackPressed() {
+		if (godotFragment != null) {
+			godotFragment.onBackPressed();
+		} else {
+			super.onBackPressed();
+		}
+	}
+
+	@Override
+	public boolean onKeyMultiple(final int inKeyCode, int repeatCount, KeyEvent event) {
+		if (godotFragment != null && godotFragment.onKeyMultiple(inKeyCode, repeatCount, event)) {
+			return true;
+		}
+		return super.onKeyMultiple(inKeyCode, repeatCount, event);
+	}
+}